Bug 15656

Summary: in_cksum computes wrong checksum
Product: Base System Reporter: Jonathan Lemon <jlemon>
Component: kernAssignee: freebsd-bugs (Nobody) <bugs>
Status: Closed FIXED    
Severity: Affects Only Me    
Priority: Normal    
Version: 4.0-CURRENT   
Hardware: Any   
OS: Any   

Description Jonathan Lemon 1999-12-23 19:00:01 UTC 
        For some data patterns, in_cksum generates a checksum of 0.
        The specification says a checksum of 0 should be transmitted
        as all ones (65535), and a transmitted checksum of 0 indicates
        that the sender did not compute a checksum.

        While 0 == 65535 in 1's complement arithmetic, this is still wrong.
        The error was discovered while doing incremental checksum
        computations on the TCP stream on an intermediate machine.

How-To-Repeat: 
        tcpdump 'tcp[16:2] == 0', (dump TCP packets with a zero checksum)
        and transmit various TCP data streams.
Comment 1 jkh freebsd_committer freebsd_triage 2000-01-17 18:42:30 UTC 
State Changed
From-To: open->closed

Submitted has rescinded PR